Polymers containing both hydrophilic and hydrophobic moieties are useful in a wide variety of applications. Unfortunately, preparation of these polymers is often difficult, inefficient, and not cost effective, particularly when it is desired to prepare the polymer in relatively high solids, low viscosity, essentially aqueous form. Preparation of these polymers have frequently been described in the prior art.
GB No. 1,052,924 discusses the polymerization of methacrylic acid with stearyl or lauryl methacrylate in a wide range of non-aqueous solvents. This method suffers from the fact that the solvents are toxic and expensive and the final form of the polymer is inconvenient to use due to the presence of these solvents.
Buscall and Corner in Colloids and Surfaces Vol. 17 (1986), pages 25 through 38, describe a method for preparing copolymers and terpolymers of acrylic acid with lauryl methacrylate. This method uses ethanol solvent, the mixtures of the monomers are added over 6 hrs, and the reaction is complete only after 48 hrs, 3 days and even up to 3 weeks. The ethanol is then removed by distillation after neutralization of the polymers in order to effect their dissolution in water.
Other methods describe the use of a mixture of water and a suitable cosolvent, where the water to cosolvent ratio is less than unity, so that the cosolvent is used in excess. This amount of cosolvent is expensive to use and time consuming and costly to remove by distillation if an essentially aqueous preparation of the polymer is desired.
For example, Buscall and Corner in EP No. 99179 describe the preparation of these copolymers in pure cosolvent, and subsequent work-up of the preparation to provide aqueous solutions by distillation and total solvent exchange. Thus, in Example 20, this procedure is followed, starting from an aqueous cosolvent mixture where the water content is in a ratio of 1.5:65 parts of water:acetone.
Hydrophobic acrylonitrile emulsions are produced in GB No. 1,351,304, in a form of non-aggregated particles, in a medium of dimethyl sulphoxide and water. The ratio of dimethyl sulphoxide to water is from 85:15 to 60:40, i.e. where the cosolvent is in excess to water.
GB No. 215,565 teaches preparation of copolymers of acrylic acid and various hydrophobic ethoxylated monomers in a mixture of isopropanol and water, where the ratio of water to isopropanol is 125:240.
In addition to using cosolvent in excess, the polymer can be produced in a limpid (clear) solution form, and this of necessity, will have a high viscosity at relatively low solids. For example, GB No. 498,383 prepares copolymers of vinyl alkyl ketones in aqueous monohydric alcohols. Although the solvent preparations are claimed to vary within wide limits, the exemplified polymers are prepared where the cosolvent is present in an amount of at least 60%. No examples are described where the water present is in excess or where the polymers are not in a limpid (clear) state.
An alternative method is to use an emulsifier to disperse the hydrophobic monomer and to subsequently obtain a copolymer having a uniform composition. The need for emulsifiers increases the cost of the polymerization process and may have a deleterious effect on the properties of the final polymer. Thus, EP No. 57,875 teaches polymerization of the hydrophobic and hydrophilic species in an aqueous medium containing an emulsifier for the hydrophobic monomer. This is exemplified by sodium dodecyl sulphate, and is essential for the preparation of homogeneous stable copolymers.
Cosolvent can be omitted altogether, when the hydrophobic moieties are more hydrophilic, by the inclusion of ethoxylate surfactant coponents in the monomers. Thus, in U.S. Pat. No. 4,559,159, polymers of surfactant type monomers having pendent hydrophobic portions are polymerized with water soluble monomers, preferably acrylic acid, to give copolymers useful in detergent compositions. A preferred method is copolymerization in aqueous solution although precipitation and suspension polymerization is described.